Calculated Ionization Potentials Research Articles

The Renner–Teller effect observed in the and electronic states of H2S+

In 1995, Balzer et al. recorded a well-resolved photoelectron spectrum of the outer valence region of H2S between 12.7 and 14.5 eV. The vibronic energies were identified with the aid of calculated ionisation potentials. Following on from this, vacuum ultraviolet pulsed-field ionisation spectroscopy was used by Hochlaf et al. in 2004 to record partially resolved rotational spectra of H2S+. Finally, in 2010, Han, Kang and Kim recorded rotationally resolved electronic spectra of the transitions of H2S+ above the barrier to linearity, by use of mass-analysed threshold ionisation photo-fragment excitation spectroscopy. By making use of new high-resolution jet-cooled electronic spectra recorded in Basel, and the rotational analyses carried out in 1972 and 1983, the different methods have been linked to provide a detailed picture of the relationship between the four different types of spectroscopy.

Quasiparticle electronic structure and optical absorption of diamond nanoparticles from ab initio many-body perturbation theory.

The excited states of small-diameter diamond nanoparticles in the gas phase are studied using the GW method and Bethe-Salpeter equation (BSE) within the ab initio many-body perturbation theory. The calculated ionization potentials and optical gaps are in agreement with experimental results, with the average error about 0.2 eV. The electron affinity is negative and the lowest unoccupied molecular orbital is rather delocalized. Precise determination of the electron affinity requires one to take the off-diagonal matrix elements of the self-energy operator into account in the GW calculation. BSE calculations predict a large exciton binding energy which is an order of magnitude larger than that in the bulk diamond.

What Dominates the Error in the CaO Diatomic Bond Energy Predicted by Various Approximate Exchange–Correlation Functionals?

In order to understand what governs the accuracy of approximate exchange-correlation functionals for intrinsically multiconfigurational systems containing metal atoms, the properties of the ground electronic state of CaO have been studied in detail. We first applied the T1, TAE(T), B1, and M diagnostics to CaO and confirmed that CaO is an intrinsically multiconfigurational system. Then, we compared the bond dissociation energies (BDEs) of CaO as calculated by 49 exchange-correlation functionals, three exchange-only functionals, and the HF method. To analyze the error in the BDEs for the various functionals, we decomposed each calculated BDE into four components, in particular the ionization potential, the electron affinity, the atomic excitation energy of the metal cation to prepare the valence state, and the interaction energy between prepared states. We found that the dominant error occurs in the calculated atomic excitation energy of the cation. Third, we compared dipole moments of CaO as calculated by the 53 methods, and we analyzed the dipole moments in terms of partial atomic charges to understand the contribution of ionic bonding and how it is affected by errors in the calculated ionization potential of the metal atom. We then analyzed the dipole moment in terms of the charge distribution among orbitals, and we found that the orbital charge distribution does not correlate well with the difference between the calculated ionization potential and electron affinity. Fourth, we examined the potential curves and internuclear distance dependence of the orbital energies of the lowest-energy CaO singlet and triplet states to analyze the near-degeneracy aspect of the correlation energy. The most important conclusion is that the error tends to be dominated by the error in the relative energies of s and d orbitals in Ca(+), and the most popular density functionals predict this excitation energy poorly. Thus, even if they were to predict the BDE reasonably well, it would be due to cancellation of errors. The effect of the cation excitation energy can be understood in terms of an orbital picture, as follows. For most functionals the predicted cation excitation energy is too small, so it is too easy to delocalize charge from the oxygen 2p orbital to the Ca(+) d orbital; this overestimates the covalency and explains why most functionals overestimate the bond energy.

Theoretical Design Study on the Electronic Structures and Phosphorescent Properties of Four Iridium(III) Complexes

The geometry structures, electronic structures, absorption, and phosphorescent properties of four Ir(III) complexes have been investigated using the density functional method. Calculations of ionization potential (IP) and electron affinity (EA) were used to evaluate the injection abilities of holes and electrons into these complexes. The result also indicates that the –CF3 substituent group on the ligand not only change the character of transition but affect the rate and balance of charge transfer. The lowest energy absorption wavelengths are located at 428 nm for 1a, 446 nm for 1b, 385 nm for 2a, and 399 nm for 2b, respectively, in good agreement with the energy gap (ΔEL-H) trend because the HOMO–LUMO transition configurations are predominantly responsible for the S0→S1 transition. 2b has the 433 nm blue emission, which might be a potential candidate for blue emitters in phosphorescent dopant emitters in organic light emitting diodes (OLEDs). The study could provide constructive information for designing novel OLEDs materials in the future.[Supplemental materials are available for this article. Go to the publisher's online edition of Molecular Crystals and Liquid Crystals to view the free supplemental file.]

Theoretical study on the electronic structures and phosphorescent properties of five bis-cyclometalated iridium(III) complexes with 2-phenylpyridinato ancillary ligand

A DFT/TDDFT study was performed on five bis-cyclometalated iridium(III) complexes with the same ancillary ligand 2-phenylpyridinato (ppy) and main ligands with different substituted groups (CH(CH3)2, CH3, H, F, and NO2). The geometry structures, electronic structures, absorption, and phosphorescent properties of the five iridium(III) complexes have been investigated. Calculations of ionization potential and electron affinity were used to evaluate the injection abilities of holes and electrons into these complexes. The lowest energy absorption wavelengths are located at 408nm for 1, 407nm for 2, 401nm for 3, 381nm for 4, and 556nm for 5, respectively, in good agreement with the HOMO–LUMO energy gaps. The lowest energy emissions of these complexes are localized at 515, 514, 516, 518, and 567nm at M052X level, respectively. The calculated results indicate that the complex 4 possibly possesses the largest kr value among the five complexes. We hope that this theoretical work can provide constructive information for designing and synthesizing novel phosphorescent materials for use in the organic light-emitting diodes.

Theoretical Studies on the Electronic Structures and Phosphorescence Properties of Three Heteroleptic Cyclometalated Iridium(III) Complexes

The geometry structures, electronic structures, absorption, and phosphorescence properties of three heteroleptic cyclometalated iridium(III) complexes have been theoretically investigated by the density functional theory (DFT) method. The highest occupied molecular orbital (HOMO) of the three complexes has the similar distributions on two main ligands. However, the lowest unoccupied molecular orbital (LUMO) of the three complexes has different distributions on different ligand fragments. Especially for 3, the LUMO is mainly composed of the picolinate auxiliary ligand. The lowest lying absorptions were calculated to be at 409, 473, and 414 nm for 1–3, respectively. By changing the conjugation length of the main ligand from 1 to 2, one can tune the emission color from green to red. The addition of sterically bulky phenolic substituents in 3 also results in an obvious red shift of the emission wavelength. The calculated results show that the absorption and emission transition character can be changed by altering the main ligands. Calculations of ionization potential (IP) and electron affinity (EA) were used to evaluate the injection abilities of holes and electrons into these complexes. The theoretical work should provide a suitable guide to the future design and synthesis of novel phosphorescent materials for use in the organic light-emitting diodes (OLEDs).

Theoretical study of electronic structures and opto-electronic properties of iridium(III) complexes containing benzoxazole derivatives and different ancillary β-diketonate ligands

Quantum-chemical method is used to study the electronic structures and opto-electronic properties of six cyclometalated iridium(III) complexes having a general formula (C^N)2Ir(LL′) [where C^N is a cyclometalating ligand (namely 2-phenyl benzoxazolato (pbo), 2-(4-chlorophenyl) benzoxazolato (cpbo), 2-phenyl-5-chlorobenzoxazolato (pcbo), 2-(3,5-difluorophenyl) benzoxazole (dfpbo)] and LL′ is an ancillary β-diketonate ligand (namely acetylacetonate (acac), dibenzoylmethanate (dbm) and 1,1,1,5,5,5-hexafluoroacetyl acetonate (hfacac). These complexes (pbo)2Ir(acac) (1), (cpbo)2Ir(acac) (2), (pcbo)2Ir(acac) (3), (dfpbo)2Ir(acac) (4), (dfpbo)2Ir(dbm) (5) and (dfpbo)2Ir(hfacac) (6) are based on benzoxazole derivatives and different β-diketonate ligands. The mobility of hole and electron are studied computationally based on the Marcus theory. Calculations of ionization potentials (IPs) and electron affinities (EAs) are used to evaluate the injection abilities of holes and electrons into these complexes. The results indicate that these complexes can be used as an electroluminescent materials.

Theoretical investigation on the electronic structures and phosphorescent properties of seven iridium(III) complexes with the different substituted 2-phenylpyridinato ancillary ligand

The geometry structures, electronic structures, absorption, and phosphorescent properties of seven iridium(III) complexes have been investigated by using the DFT/TDDF methods. Calculations of ionization potential and electron affinity were used to evaluate the injection abilities of holes and electrons into these complexes. The lowest energy emissions of these complexes are localized at 662, 583, 502, 518, 527, 536, and 538nm, respectively, for complexes 1–7, simulated in CH2Cl2 medium at M052X level. The calculated results indicate that the complex 5 possibly possesses the largest kr value among the seven complexes.

Theoretical studies on electronic structures and photophysical properties of anthracene derivatives as hole-transporting materials for OLEDs

The electronic structures and photophysical properties of anthracene derivatives as hole-transporting materials (HTM) in OLEDs have been studied by DFT and TD-DFT methods. Thiophene and triphenylamine (TPA) moieties are used as substituents in anthracene based HTMs providing FATn and FAPn compounds (n=1–2), respectively. The calculated electronic levels by B3LYP show proper energy matching of FAPn and hole-injecting layer (HIL), indicating that the hole-transports of the FAPn compounds are better than the FATn compounds. The photophysical properties calculated by TD-B3LYP elucidate that TPA in FAPn compounds acts as electron donating group and induces charge transfer character in the absorptions. Furthermore, the calculated ionization potential (IP), electron affinity (EA) and reorganization energies also revealed that the extended FAP2 compound has the highest charge-transporting ability among the studied compounds. The calculated results are consistent to our experimental observations showing that FAP2 exhibits bright fluorescence with highest quantum yield in electroluminescent devices. Understanding of these properties is useful for further design of new HTMs of desired properties, such as high efficiency and stability.

Geometrical approach to the atomic spectra theory. The helium atom

New equations for helium spectra calculations are obtained within geometrical interpretation of quantum mechanics suggested by the author earlier. The main idea of the above interpretation is that atoms can be considered not as the systems with many electrons but as a microscopic topological defect of the physical space-time without any point-like particles inside. The groups of symmetry transformations of such defects are suggested to be isomorphic to the symmetry groups of atoms with many identical electrons (permutation group, for example). New equations were derived within approximation that is similar to the one in the self consistent field theory of Hartree-Fok, but these equations differ strongly from Hartree-Fock equations. Numerical calculations of ionization potentials for para—and orto—helium lead to results that are in a good agreement with experiment.

Geometrical Approach in Atomic Physics: Atoms of Hydrogen and Helium

The hypothesis was earlier suggested by the author where all micro-objects are considered as specific distortions of the physical space-time pseudo-Euclidean geometry, namely, as closed topological 4-manifolds. The foundation of the hypothesis is a geometrical interpretation of the basic equation of quantum mechanics for classical (not quantized) wave fields -- the Dirac equation for free particle. Such hypothesis does not contradict to any physical laws and experimental facts and gives firstly an opportunity to explain qualitatively within classical notions (geometrical) the so called “paradoxical” properties of quantum particles such as wave-corpuscular duality, appearance of probabilities in the quantum mechanics formalism, spin, EPR-paradox.To demonstrate prospects for suggested geometrical approach the author early attempted to find new dynamic equations other than known quantum-mechanical ones for atomic spectra calculations. In this work above investigation is being continued on a more rigorous basis, representing a new geometrical interpretation of the equation for hydrogen atoms. Results of calculations of ionization potentials for helium atom are in agreement with experimental data.

Theoretical study of the effects of amino acids on one-electron oxidation of a nucleobase: adenine residue can be a hole-trapping site

DNA damage by oxidative stress has been extensively investigated, but the effect of interaction with histone protein on the DNA oxidation has not been well-understood. The effects of amino acids on DNA oxidation induced by one-electron oxidants were examined by ab initio molecular orbital calculation at Hartree-Fock 6-31G* level. The calculated ionization potentials of nucleobases suggest that guanine is protected by interaction with amino acids from oxidative damage, whereas oxidation of adenine is enhanced through interaction with several kinds of amino acids. These findings suggest that adenine can be easily oxidized under the interaction with certain amino acid in chromatin rather than guanine, which can be most easily oxidized in isolated DNA. The effect of amino acids on DNA oxidation may explain the mutation at adenine residue induced by oxidative stress due to ultraviolet A irradiation.

Theoretical study on electronic structures and phosphorescence properties of four tris-cyclometalated iridium(III) complexes

The geometry structures, electronic structures, absorption, and phosphorescence properties of four tris-cyclometalated iridium(III) complexes IrL3, that is, 1 (L = 2-(4,6-difluorophenyl)pyridinato,N,C2′), 2 (L = 2-(4,6-difluorophenyl)pyridinato,N,C2′-5-phenyl), 3 (L = 2-(4,6-difluorophenyl)pyridinato,N,C2′-5-(p-tolyl)), and 4 (L = 2-(4,6-difluorophenyl) benzo[h]isoquinoline), have been investigated under the framework of the time-dependent density functional theory approach. For assumed 2 and 3, the emission energies are nearly the same, consistent with their similar HOMO−LUMO energy gaps. The calculated lowest energy emissions are localized at 523, 605, 616, and 642 nm for 1, 2, 3, and 4, respectively. Calculations of ionization potential and electron affinity were used to evaluate the injection abilities of holes and electrons into these complexes. For 2, the calculated results evidenced a larger 3MLCT contribution (27.0%), a large S0 → S1 transition dipole moment ([Formula: see text]) of 1.43 D, and a small S1−T1 splitting energy ([Formula: see text]) of 0.33 eV, which could result in a large radiative decay rate (kr). We hope that this theoretical work can provide a suitable guide to the future design and synthesis of novel phosphorescent materials for use in the organic light-emitting diodes.

Molecular orbital studies (hardness, chemical potential and electrophilicity), vibrational investigation and theoretical NBO analysis of 4-4′-(1H-1,2,4-triazol-1-yl methylene) dibenzonitrile based on abinitio and DFT methods

The Fourier transform infrared (FTIR) and FT Raman (FTR) of 4-4′-(1H-1, 2, 4-triazol-1-yl methylene) dibenzonitrile (4-HTMDBN) have been recorded and analyzed. The equilibrium geometry harmonic vibrational frequencies have been investigated with the help of standard HF and DFT methods with 6-31G(d,p) as basis set. The assignments of the vibrational spectra have been carried out with the help of normal co-ordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). Theoretical simulations of the FTIR and FTR spectra of the title compound have been calculated. The 1H and 13C Nuclear Magnetic Resonance (NMR) chemical shifts of the molecule were calculated by the Gauge including atomic orbital (GIAO) method. The stability of the molecule has been analyzed using natural bond orbital (NBO) analysis. The linear polarizability (α) and the first order hyperpolarizability (β) values of the investigated molecule have been computed using HF/DFT/6-31G(d,p) methods on the finite field approach. UV–Vis spectrum of the compound is recorded and the electronic properties such as HOMO and LUMO energies, are performed. The directly calculated ionization potential (IP), electron affinity (EA), electronegativity (χ), electrophilicity index (ω), hardness (η) and chemical potential (ρ) are all correlated with the HOMO and LUMO energies with their molecular properties. Mulliken population analysis on atomic charges, molecular electrostatic potential maps (MEP) and thermodynamical properties of title compound at different temperature have been calculated.

NBO, NMR, UV, FT-IR, FT-Raman spectra and molecular structure (monomeric and dimeric structures) investigation of 4-Chloro-3,5-Xylenol: A combined experimental and theoretical study

In this work, a joint experimental (FTIR and FT-Raman) and theoretical (DFT and ab initio) study on the structure and the vibrations of 4-Chloro-3,5-Xylenol (CXL) are compared and analyzed. CXL is a chlorinated phenolic antiseptic which is a bactericide against most gram-positive bacteria. The first hyperpolarizability (β0) of this novel molecular system and related non-linear properties of CXL are calculated using HF/6-311++G(d,p) method on the finite-field approach. The energy and oscillator strength calculated using absorption spectra (UV–Vis spectrum), this spectral analysis confirms the charge transfer of the molecule. The theoretical 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by Gauge Including Atomic Orbital (GIAO) method, to analyze the molecular environment as well as the delocalization activities of electron clouds. The directly calculated ionization potential (IP), electron affinity (EA), electronegativity (χ), chemical hardness (η), first electron excitation energy (τ) and electrophilicity index (ω) as well as local reactivity (S) analyzed using HOMO and LUMO energies; the energy band gap are also determined. NBO analysis shows that charge in electron density(ED) in the σ* and π* antibonding orbitals and E(2) energies confirms the occurrence of ICT (Intramolecular Charge Transfer) within the molecule. Inter molecular hydrogen bonds exist between –OH group, give the evidence for the formation of dimer entities in the title molecule. The influences of chlorine atom, hydroxyl group and methyl group on the geometry of benzene and its normal modes of vibrations (monomer and dimer of CXL) have also been discussed. Finally the calculated results were applied to simulate Infrared and Raman spectra of the title molecule which show good agreement with observed spectra.

Structures, relative stabilities, and electronic properties of potassium clusters Kn (13 ⩽ n ⩽ 80)

We report the global minimum (GM) structures, energetic and electronic properties of Kn clusters with up to 80 atoms, obtained by combining basin hopping unbiased optimizations (based on a many-body empirical potential) with subsequent reoptimization of several candidate structures employing a density functional theory method which accounts for van der Waals dispersion interactions (vdW-DFT). A comparison with other alkali cluster systems shows that the GM structures of Kn coincide with those of Nan more often than with those of Csn clusters. Nevertheless, the inclusion of dispersion interactions produces for several clusters changes in the GM structures, which become either identical to those of Csn clusters, or completely novel (i.e. not reported for other alkali systems). Many GM structures are based on poly-icosahedral packing; some others contain Kasper polyhedral units with disclination lines. Atoms with a low coordination number (or adatoms) are avoided in the GM structures following a geometric shell closing: such additional atom is instead inserted into the outermost atomic shell of the cluster. The calculated ionization potentials, electron affinities and HOMO–LUMO gaps are found to reproduce perfectly the electron shell closings observed in photoionization measurements. The electric dipole moments of most clusters are close to zero, a distinguishing feature of metallicity previously observed for Nan clusters. However, some clusters like K26, K47 or K49 have sizable electric dipole moments. The cluster stabilities are found to explain the experimental abundances inferred from mass spectra. The enhanced stabilities (magic numbers) can be interpreted in terms of electron shell closing effects for the smaller clusters and of geometrical packing effects for the larger clusters. Although there is not a sharply defined critical size separating both regimes, it is estimated to be around 55 atoms.

GWcalculations using the spectral decomposition of the dielectric matrix: Verification, validation, and comparison of methods

In a recent paper [Nguyen et al., Phys. Rev. B 85, 081101(R) (2012)] we presented an approach to evaluate quasiparticle energies based on the spectral decomposition of the static dielectric matrix. This method does not require the calculation of unoccupied electronic states or the direct diagonalization of large dielectric matrices, and it avoids the use of plasmon-pole models. The numerical accuracy of the approach is controlled by a single parameter, i.e., the number of eigenvectors used in the spectral decomposition of the dielectric matrix. Here we present a comprehensive validation of the method, encompassing calculations of ionization potentials and electron affinities of various molecules and of band gaps for several crystalline and disordered semiconductors. We demonstrate the efficiency of our approach by carrying out $GW$ calculations for systems with several hundred valence electrons.

Direct ΔMBPT(2) method for ionization potentials, electron affinities, and excitation energies using fractional occupation numbers

A direct method (D-ΔMBPT(2)) to calculate second-order ionization potentials (IPs), electron affinities (EAs), and excitation energies is developed. The ΔMBPT(2) method is defined as the correlated extension of the ΔHF method. Energy differences are obtained by integrating the energy derivative with respect to occupation numbers over the appropriate parameter range. This is made possible by writing the second-order energy as a function of the occupation numbers. Relaxation effects are fully included at the SCF level. This is in contrast to linear response theory, which makes the D-ΔMBPT(2) applicable not only to single excited but also higher excited states. We show the relationship of the D-ΔMBPT(2) method for IPs and EAs to a second-order approximation of the effective Fock-space coupled-cluster Hamiltonian and a second-order electron propagator method. We also discuss the connection between the D-ΔMBPT(2) method for excitation energies and the CIS-MP2 method. Finally, as a proof of principle, we apply our method to calculate ionization potentials and excitation energies of some small molecules. For IPs, the ΔMBPT(2) results compare well to the second-order solution of the Dyson equation. For excitation energies, the deviation from equation of motion coupled cluster singles and doubles increases when correlation becomes more important. When using the numerical integration technique, we encounter difficulties that prevented us from reaching the ΔMBPT(2) values. Most importantly, relaxation beyond the Hartree-Fock level is significant and needs to be included in future research.

Efficient blue‐emitting Ir(III) complexes with phenyl‐methyl‐benzimidazolyl and picolinate ligands: A DFT and time‐dependent DFT study

AbstractThe series of heteroleptic cyclometalated Ir(III) complexes for organic light‐emitting display application have been investigated theoretically to explore their electronic structures and spectroscopic properties. The geometries, electronic structures, and the lowest‐lying singlet absorptions and triplet emissions of Ir‐(pmb)3 and theoretically designed models Ir‐(Rpmb)2pic were investigated with density functional theory (DFT)‐based approaches, where pmb = phenyl‐methyl‐benzimidazolyl, pic = picolinate, and R = H/F. Their structures in the ground and excited states have been optimized at the DFT/B3LYP/LANL2DZ and TDDFT/B3LYP/LANL2DZ levels, and the lowest absorptions and emissions were evaluated at B3LYP and M062X level of theory, respectively. The mobility of holes and electrons were studied computationally based on the Marcus theory. Calculations of ionization potentials were used to evaluate the injection abilities of holes into these complexes. The reasons for the higher electroluminescence efficiency and phosphorescence quantum yields in Ir‐(Rpmb)2pic than in Ir‐(pmb)3 have been investigated. The designed moleculars are expected to be highly emissive in pure‐blue region. © 2013 Wiley Periodicals, Inc.

Comparison of in vivo and in vitro antioxidative parameters for eleven food factors

In vivo antioxidative activity assays against reactive oxygen species generated in mitochondria, together with in vitro two radical-scavenging assays, electrochemical measurements, and theoretical calculations of ionization potentials (IP), were carried out for eleven food factors. Lycopene, with the smallest IP value, showed the highest anti-apoptotic activity.